<!DOCTYPE html>
<html>
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>

  <body>
    <div id="app"></div>

    <template id="my-app">
      <h2>{{message}}</h2>
      <component-a></component-a>
    </template>

    <template id="component-a">
      <h2>我是component-a局部组件</h2>
    </template>
    <script src="../js/vue.js"></script>
    <script>
      const ComponentA = {
        template: "#component-a",
      };
      const App = {
        template: "#my-app",
        components: {
          //key： 组件名称
          //value：组件对象
          ComponentA,
        },
        data() {
          return {
            message: "Hello World",
          };
        },
      };

      const app = Vue.createApp(App);

      app.mount("#app");
    </script>
  </body>
</html>
